Plasma processes have become important in the manufacture of semiconductor devices such as integrated circuits. Low pressure glow discharge plasmas are used in the anisotropic etching of fine-line patterns, and plasmas are routinely used for low temperature deposition of insulating and passivating layers such as silicon nitride.
Typical plasma reactors for microelectronics applications comprise a low pressure chamber, a source of gas to be converted to plasma, and a source of energy to convert the gas to plasma. Among the most popular of new plasma generators are those based on electron cyclotron resonance heating. In ECR reactors microwaves from an external source are launched through a dielectric window into the chamber to excite the gas within the chamber and thus create a plasma. Such generators permit separate control of plasma generation and ion transport. Thus, for example, in etching, ion flux and ion energy can be controlled separately to optimize throughput, selectivity and anisotropy while minimizing ion-induced atomic displacement damage.
Unfortunately plasmas are not well understood and their behavior can fluctuate in seemingly random ways which can greatly affect their useful properties. Specifically, by virtue of their non-linear properties, plasmas are prone to instability, bistability, and hysteresis which can deteriorate the reproducibility of critical semiconductor manufacturing processes. Present control schemes based on maintaining constant pressure have not been adequate to prevent serious fluctuations in etch rate and deposition rate in plasma-based semiconductor manufacturing processes.